The present disclosure relates to a coil component having adjustable impedance.
In recent years, electronic devices such as portable phones, home appliances, personal computers (PCs), personal digital assistants (PDAs), liquid crystal displays (LCDs), navigation systems, and the like have gradually been digitalized and provided with faster processing speeds. Since these electronic devices are sensitive to external stimuli, low abnormal voltage and high frequency noise may be present in the internal circuits of the electronic devices, and may cause damage to circuits and signal distortion.
Switching voltages generated in circuits, power noise included in power supply voltages, unnecessary electromagnetic signals or noises, and the like may cause such abnormal voltages and noise. As a means for preventing the abnormal voltages and the high frequency noise from flowing into circuits, coil components have widely been used.
In particular, high speed interfaces such as universal serial buses (USBs) 2.0, USBs 3.0, and high-definition multimedia interface (HDMI) have adopted a differential signal system that transmits differential signals (differential mode signals) using a pair of signal lines, unlike a general single-end transmission system. Thus, the differential signal transmission system uses a common mode filter (CMF) for removing common mode noise.
When a capacitive element such as a CMF is provided on a transmission line, a high frequency signal or a high speed pulse signal transmitted through the transmission line may be reflected or attenuated. In the case in which the capacitive element is provided on the transmission line, characteristic impedance (Zo) at an insertion position of the capacitive element may be deteriorated by a capacitance component of the capacitive element, and as a result, impedance matching may not occur in a corresponding position.
When the transmission line has a portion in which the impedance matching does not occur, since a non-matching portion of characteristic impedance (Zo) may be reflected, return loss may occur. As a result, the signal may be significantly attenuated, and unnecessary radiation may occur within the transmission line by the reflection, which is a cause of noise generation.
Thus, characteristic impedance (Zo) of capacitive coil components used as a variety of electrostatic discharge (ESD) preventing components including a CMF is required to match impedance of the signal transmitting system into which the coil components are inserted.
Characteristic impedance (Zo) in the coil component may be adjusted by altering line width of a spiral coil conductor constituting the coil component, interlayer distance between the coil conductors, dielectric constant of a material present between the coil conductors, or the like. For example, when a distance between patterns is reduced or the interlayer distance between the coil conductors is decreased by forming the line width of the coil conductor to be significantly wide, or the dielectric constant of the material present between the coil conductors is increased, a parasitic capacitance component may be increased, whereby characteristic impedance (Zo) may be decreased.
However, the adjustment of characteristic impedance Zo by the dielectric constant naturally has a limitation due to the characteristics of the material, and it is also difficult to adjust characteristic impedance Zo by the interlayer distance between the coil conductors or the line width of the coil conductor due to a recent trend for thinness and lightness, and a fine pattern of the coil component.